40
isoEV425_D00126_09_M_XXEN/03.2019
7. Data access using the Modbus RTU protocol
Requests to the ISOMETER® can be made using the function code 0x03 (read
multiple registers) or the command 0x10 (write multiple registers). The ISO-
METER® generates a function-related answer and sends it back.
7.1
Reading out the Modbus register from the ISOMETER®
The required Words of the process image can be read out from the "Holding
registers" of the ISOMETER® using the function code 0x03. For this purpose,
the start address and the number of the registers to be read out have to be en-
tered. Up to 125 Words (0x7D) can be read out by one single request.
7.1.1
Master sends a command to the
ISOMETER®
In the following example, the master of the ISOMETER® with address 3
requests the contents of register 1003. The register contains the channel
description of measuring channel 1.
Byte Name
Example
Byte 0
ISOMETER® Modbus address
0x03
Byte 1
Function code
0x03
Byte 2, 3
Start address
0x03EB
Byte 4, 5
Number of registers
0x0001
Byte 6, 7
CRC16 Checksum
0xF598